Whatever the beast may be, perhaps a bear, a large stag, a timberwolf, a cougar, perhaps some otherworldly monster that Medic had never seen before... it's in rut and has eyes for him. Maybe the beast hasn't been able to find a female of its kind to mate with and decides he's the next best thing, maybe the beast has a fixation on humans. It easily manages to tear his pants off and wastes no time pushing inside, without lube no less. Paying no mind to Medic screeching underneath in pain and fear of getting killed but knowing what's happening instead. I'm sure he'll end up enjoying it before the fun's over, maybe the ride gets a little easier thanks to the precum (and blood) lubing him up after a while, maybe he's a bit of a masochist, maybe it's managed to find his prostate. Those screams and whimpers turn into moans and huffs, Medic rolling his hips back against the beast to take in as much as he can fit. Gets cum-and-dumped and left in the dirt and foliage all scratched and bruised up, cum leaking out of his hole for his troubles. It takes a bit for him to recover enough to shakily stand up and limp back to the base, not bothering to put his pants back on as they're ruined beyond salvaging.